Image display apparatuses have been proposed that use a current-control type organic EL (Electroluminescent) device having a function of emitting light through the recombination of electrons and positive holes injected into the light emitting layer.
In an image display apparatus of this type, each pixel includes a thin film transistor (TFT) which is formed of, for example, amorphous silicon or polycrystalline silicon, and an organic light emitting diode (OLED), which is one of the organic EL devices. The brightness of the pixel is controlled by setting its current to an appropriate value.
For example, an active matrix image display apparatus with a plurality of pixels, each having a light emitting device connected in series with a driving transistor such as TFT, suffers from brightness fluctuations due to changes in current flowing through the light emitting device. Several technologies have been disclosed to counteract this phenomenon. One such technology involves detecting in advance the threshold voltage of the driving transistor so that the current flowing through the light emitting device can be controlled based on the threshold voltage (see, for example, Non-Patent Document 1). On the basis of the technology, specific circuitry has also been disclosed (see, for example, Non-Patent Document 2).    [Non-Patent Document 1] R. M. A. Dawson et al., “Design of an Improved Pixel for a Polysilicon Active-Matrix Organic LED Display,” in SID Tech. Dig., 1998, pp. 11-14.    [Non-Patent Document 2] Ono et al., “Pixel Circuit for a-Si AM-OLED,” IDW'03 (2003), pp. 255-258.